Method and apparatus for removing acoustic incident signal

ABSTRACT

A method of removing a signal from among received signals, the method including: filtering the received signals; detecting a time band of the filtered received signals where an energy value of the filtered received signals exceeds a reference energy value; and applying a gain value to one or more received signals, from among the received signals, in the detected time band.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application is a Continuation application of U.S. application Ser.No. 12/872,605 filed Aug. 31, 2010, which claims priority from KoreanPatent Application No. 10-2010-0002751, filed on Jan. 12, 2010 in theKorean Intellectual Property Office, the disclosure of which isincorporated herein in its entirety by reference.

BACKGROUND

1. Field

Methods and apparatuses consistent with exemplary embodiments relate toa method and apparatus for removing a signal, and more particularly, toa method and apparatus for effectively removing an acoustic incidentsignal by decreasing a reference energy value by using a frequencyweighting filter.

2. Description of the Related Art

An unexpected acoustic incident may occur while talking to anotherperson through a digital device, such as a mobile terminal or anInternet phone. The acoustic incident refers to a large noise that issuddenly heard during a phone call. When exposed to the acousticincident, a user experiences a symptom, such as acoustic damage,temporary acoustic disability, or a headache, which is called anacoustic shock.

In order to remove the acoustic incident that may occur during the phonecall, a technology which removes a tone signal having a large volumethat exceeds a predetermined reference value is used. However, in anactual digital device, the acoustic incident is generated in the overallfrequency band in the form of white noise, instead of in the form of thetone signal. Accordingly, the technology which removes the tone signalhaving the large volume cannot effectively remove the acoustic incidentgenerated during the phone call.

SUMMARY

Exemplary embodiments provide a method and apparatus for removing anacoustic incident signal that is generated during a phone call byreducing a reference energy value using a frequency weighting filter.

According to an aspect of an exemplary embodiment, there is provided amethod of removing a signal from among received signals, the methodincluding: filtering the received signals; detecting a time band of thefiltered received signals where an energy value of the filtered receivedsignals exceeds a reference energy value; and applying a gain value toone or more received signals, from among the received signals, in thedetected time band.

The filtering the received signals may include filtering the receivedsignals by using a frequency weighting filter.

The frequency weighting filter may apply increasing weights from a lowfrequency band to a high frequency band, wherein the weight may be apositive real number less than or equal to 1.

The filtering the received signals may include filtering the receivedsignals in a frequency band of 4 KHz or lower by using the frequencyweighting filter.

The method may further include outputting the one or more receivedsignals to which the gain value is applied and remaining receivedsignals having an energy value that does not exceed the reference energyvalue after being filtered, together.

The detecting the time band may include: calculating an average energyvalue of the filtered received signals in a time domain, according toframes; and detecting a time band of a frame in which the average energyvalue of the filtered received signals is greater than the referenceenergy value.

The method may further include calculating a value for adjusting theaverage energy value of the filtered received signals to the referenceenergy value in the detected time band, according to frames, wherein theapplying the gain value may include applying the calculated value on thereceived signals in each frame as the gain value.

The gain value may be a positive real number less than 1.

According to an aspect of another exemplary embodiment, there isprovided an apparatus for removing a signal from among received signals,the apparatus including: a filter unit which filters the receivedsignals; an acoustic incident signal section detecting unit whichdetects a time band of the filtered received signals where an energyvalue of the filtered received signals exceeds a reference energy value;and a gain applying unit which applies a gain value to one or morereceived signals, from among the received signals, in the detected timeband.

According to an aspect of another exemplary embodiment, there isprovided a computer readable recording medium having recorded thereon aprogram for executing a method of removing a signal from among receivedsignals, the method including: filtering the received signals; detectinga time band of the filtered received signals where an energy value ofthe filtered received signals exceeds a reference energy value; andapplying a gain value to one or more received signals, from among thereceived signals, in the detected time band.

According to an aspect of another exemplary embodiment, there isprovided a method of removing a signal from among received signals, themethod including: filtering the received signals; detecting a time bandof the filtered received signals where an energy value of the filteredreceived signals exceeds a reference energy value; and reducing a volumeof a signal, from among the received signals, at the detected time bandto be less than another signal that is not at the detected time band.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages will become more apparent bydescribing in detail exemplary embodiments thereof with reference to theattached drawings in which:

FIG. 1 is a block diagram illustrating an apparatus for removing anacoustic incident signal, according to an exemplary embodiment;

FIG. 2 is a block diagram illustrating an apparatus for removing anacoustic incident signal, according to another exemplary embodiment;

FIG. 3 is a graph for describing frequency characteristics of afrequency weighting filter used in a filter unit of FIG. 1 or 2;

FIG. 4 shows graphs for comparing a received signal before and afterpassing through the filter unit of FIG. 1 or 2;

FIG. 5 is a graph showing a signal output from an output unit accordingto an exemplary embodiment; and

FIG. 6 is a flowchart illustrating a method of removing an acousticincident signal, according to an exemplary embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, exemplary embodiments will be described more fully withreference to the accompanying drawings, in which like reference numeralsrefer to like elements throughout.

FIG. 1 is a block diagram illustrating an apparatus 100 for removing anacoustic incident signal, according to an exemplary embodiment.Referring to FIG. 1, the apparatus 100 includes a filter unit 110, anacoustic incident signal section detecting unit 120, and a gain applyingunit 130.

The filter unit 110 filters signals received from another terminalthrough a receiving terminal, such as a phone. The filter unit 110applies, on the received signals, a frequency weighting filter fordifferent weights according to frequency bands.

While the received signals heard from the receiving terminal aretransmitted from the ear hole to the eardrum, resonance due to an earcanal is generated near 3 KHz. Thus, during a phone call, an ear of aperson is sensitive to a signal in a frequency band from 1 KHz to 4 KHz.In such a frequency band from 1 KHz to 4 KHz, voice signals of a personare mainly distributed in a low frequency band of 2 KHz or below, andacoustic incident signals are mainly distributed in a middle and highfrequency band of 2 KHz or above. In other words, the voice signals andthe acoustic incident signals exist in different frequency bands.

According to the current exemplary embodiment, a voice signal and anacoustic incident signal are separated from each other based on the factthat the voice signal and the acoustic incident signal are mainlydistributed in different frequency bands. In other words, the filterunit 110 gives different weights to the voice signal and the acousticincident signal by using the frequency weighting filter giving differentweights according to frequency bands.

Here, the weight may be a real number equal to or smaller than 1. Also,the frequency weighting filter used by the filter unit 110 may give ahigher weight from a low frequency band to a high frequency band. Inother words, the filter unit 110 may give a high weight closer to 1 to asignal in the high frequency band near 4 KHz, and give a low weightcloser to 0 to a signal in the low frequency band near 0 Hz, therebypassing through the acoustic incident signal, from among the receivedsignals, which is distributed in the high frequency band as the acousticincident signal is, and reducing the size of the voice signal, fromamong the received signals, which is distributed in the low frequencyband. Accordingly, when the received signals pass through the filterunit 110, the acoustic incident signal in the high frequency band isoutput as the acoustic incident signal and the voice signal in the lowfrequency band is output with a reduced size. Thus, a size differencebetween the voice signal and the acoustic incident signal is increased.

As described above, the ear of the person is sensitive to a signal in afrequency band of 4 KHz or lower. Accordingly, unlike an audio speaker(not shown), a speaker (not shown) for outputting a phone call signalgenerally has a frequency band of 4 KHz or lower. Accordingly, thefrequency weighting filter used by the filter unit 110 may also beapplied to a signal in a frequency band of 4 KHz or lower.

The filter unit 110 transmits the filtered received signals to theacoustic incident signal section detecting unit 120.

The acoustic incident signal section detecting unit 120 converts thefiltered received signal in a frequency domain to a signal in a timedomain. Furthermore, the acoustic incident signal section detecting unit120 detects a time section in which the acoustic incident signal exists,from the filtered received signals.

In order to detect the time section from the filtered received signals,the acoustic incident signal section detecting unit 120 divides thefiltered received signals according to frames, and calculates an averageenergy value by calculating a root mean square (RMS) of the filteredreceived signals in each frame. The average energy value according toframes may be obtained by Equation 1 below:

$\begin{matrix}{\sqrt{\frac{1}{N}{\sum\limits_{i = 1}^{N}\;{x^{2}(i)}}},} & \lbrack {{Equation}\mspace{14mu} 1} \rbrack\end{matrix}$where x(i) denotes a received signal filtered by the frequency weightingfilter, and N is a frame size for calculating the RMS.

The acoustic incident signal section detecting unit 120 compares theaverage energy value obtained according to frames with a fixed thresholdvalue, i.e., a predetermined reference energy value. When the averageenergy value exceeds the reference energy value, the acoustic incidentsignal section detecting unit 120 determines that the filtered receivedsignal in the frame having that average energy value is the acousticincident signal. The acoustic incident signal section detecting unit 120calculates a time value of the frame including the filtered receivedsignal having the average energy value higher than the reference energyvalue.

The reference energy value may differ based on the filtered receivedsignal having the average energy value that will be determined as theacoustic incident signal. Also, the reference energy value may differaccording to a type of the frequency weighting filter used by the filterunit 110. By using the frequency weighting filter that gives a smallerweight to the voice signal in the low frequency band, the size of thevoice signal in the low frequency band is reduced more than the originalsize. Accordingly, the acoustic incident signal section detecting unit120 may use a smaller reference energy value to classify whether thefiltered received signal is the acoustic incident signal or the voicesignal. As the reference energy value decreases, the acoustic incidentsignal is easily detected.

The acoustic incident signal section detecting unit 120 determines avalue for reducing the average energy value that is greater than thereference energy value, i.e., determines a value for reducing theaverage energy value of the filtered received signal determined to bethe acoustic incident signal to the reference energy value as a gainvalue. The gain value may be a real number between 0 and 1 to reduce theaverage energy value of the acoustic incident signal to the referenceenergy value.

The acoustic incident signal section detecting unit 120 obtains a timeband of the acoustic incident signal in a frame unit. Since the averageenergy value of the acoustic incident signal may differ according toframes, the gain value for reducing the average energy value of theacoustic incident signal to the reference energy value may also differaccording to frames. Accordingly, the acoustic incident signal sectiondetecting unit 120 may obtain the gain value according to frames.

The acoustic incident signal section detecting unit 120 provides, to thegain applying unit 130, the time band of the acoustic incident signalhaving the higher average energy value than the reference energy valuefrom among the filtered received signals, and the gain values to beapplied to each frame.

The gain applying unit 130 receives information about the time band andthe gain values to be applied to each frame from the acoustic incidentsignal section detecting unit 120. Also, the gain applying unit 130receives the received signals that do not pass through the filter unit110. The gain applying unit 130 applies the gain values to the receivedsignals by using the information received from the acoustic incidentsignal section detecting unit 120. In other words, the gain applyingunit 130 adjusts the size of the acoustic incident signal by applyingthe gain values according to frames to the received signals in thecorresponding frame.

Since the filter unit 110 filters the acoustic incident signal that ismostly distributed in middle and high frequency bands by giving theacoustic incident signal a relatively higher weight (e.g., a weightclose to 1), energy values of the received signal in the middle and highfrequency bands before and after being filtered by the filter unit 110are similar. Accordingly, when the gain value for reducing the averageenergy value of the filtered received signal to the reference energyvalue is applied to the received signal, the size of the received signalin the middle and high frequency bands, which are multiplied by the gainvalue, is similar to the reference energy value.

Since the average energy value of the signal in the low frequency bandfrom among the filtered received signals does not exceed the referenceenergy value, the received signal in the low frequency band is notmultiplied by the gain value. Accordingly, the voice signal that ismostly distributed in the low frequency band maintains its originalsize.

By applying the frequency weighting filter on the received signals, thesize of the voice signal is reduced, and thus the reference energy valueis also reduced according to the reduced size of the voice signal. Inthis case, the acoustic incident signal is multiplied by a decreasedgain value to reduce the average energy value of the acoustic incidentsignal to the reference energy value. As described above, the gain valueis a real number between 0 and 1.

As described above, the size of the voice signal from among the receivedsignals is maintained, while the size of the acoustic incident signalfrom among the received signals is reduced to the reference energy valueby being multiplied by the gain value. Accordingly, when the receivedsignals pass through the gain applying unit 130, the size of theacoustic incident signal is less than the size of the voice signal.

As such, according to the current exemplary embodiment, the energy valueof the voice signal in the low frequency band from among the receivedsignals may be reduced by using the frequency weighting filter. Also,since the energy value of the voice signal is reduced, the referenceenergy value for separating the acoustic incident signal and the voicesignal from each other may be small.

Also, according to the current exemplary embodiment, the value forreducing the energy value of the acoustic incident signal in the middleand high frequency bands to the reference energy value is obtained asthe gain value, and the gain value is applied to the received signals.Thus, the energy size of the acoustic incident signal may be smallerthan that of the voice signal, from among the received signals.

FIG. 2 is a block diagram illustrating an apparatus 200 for removing anacoustic incident signal, according to another exemplary embodiment.Referring to FIG. 2, the apparatus 200 includes a decoding unit 210, afilter unit 220, an acoustic incident signal section detecting unit 230,a gain applying unit 240, and an output unit 250. The filter unit 220,the acoustic incident signal section detecting unit 230, and the gainapplying unit 240 of the apparatus 200 are respectively similar to thefilter unit 110, the acoustic incident signal section detecting unit120, and the gain applying unit 130 of the apparatus 100, and thusdetailed descriptions thereof will not be repeated.

The decoding unit 210 restores pulse code modulation (PCM) signals bydecoding encoded signals received through a digital device, such as amobile terminal or an Internet phone. The decoding unit 210 transmitsthe PCM signals to each of the filter unit 220 and the gain applyingunit 240.

The filter unit 220 filters the PCM signals by using a frequencyweighting filter, and transmits the filtered PCM signals to the acousticincident signal section detecting unit 230.

The acoustic incident signal section detecting unit 230 obtains anenergy value of each of the filtered PCM signals in frame units.Furthermore, the acoustic incident signal section detecting unit 230obtains a frame of a signal having an average energy value greater thana reference energy value, from among the filtered PCM signals, andprovides, to the gain applying unit 240, a time band of the obtainedframe. Also, the acoustic incident signal section detecting unit 230obtains a gain value for adjusting the energy value of the filtered PCMsignals in the time band in which the average energy value is greaterthan the reference energy value, to the reference energy value in aframe unit, and provides, to the gain applying unit 240, the gain value.

The gain applying unit 240 receives the decoded PCM signal from thedecoding unit 210, and receives information about the time band and thegain value to be applied to the PCM signals in the time band from theacoustic incident signal section detecting unit 230. The gain applyingunit 240 applies the gain value to the PCM signals according to frames.Furthermore, the gain applying unit 240 transmits the PCM signalsmultiplied by the gain value to the output unit 250. Since a voicesignal from among the PCM signals is not multiplied by the gain value,the gain applying unit 240 transmits the PCM signal, i.e., an acousticincident signal, which is multiplied by the gain value, and the voicesignal to which the gain value is not applied to the output unit 250.

The output unit 250 converts a digital signal to an analog signal, andoutputs the analog signal through a speaker (not shown). The output unit250 outputs the acoustic incident signal to which the gain value isapplied and the voice signal to which the gain value is not appliedtogether.

FIG. 3 is a graph for describing frequency characteristics of thefrequency weighting filter used in the filter unit 110 or 220 of FIG. 1or 2. Referring to FIG. 3, a horizontal axis indicates a frequency and avertical axis indicates a weight. The weight is a real number less thanor equal to 1, and the frequency is normalized to 1.

Referring to the graph of FIG. 3, it can be seen that the frequencyweighting filter applies different weights to received signals accordingto frequency bands. In the graph of FIG. 3, a weight applied to a signalin middle and high frequency bands is closer to 1, and a weight appliedto a signal in a low frequency band is less than 1 and closer to 0. Inother words, the weight applied to the received signals is increasedfrom the low frequency band to the high frequency band.

Accordingly, when the frequency weighting filter according to FIG. 3 isapplied to the received signals, an energy size of a voice signal, whichis mostly distributed in the low frequency band, is reduced, and anenergy size of an acoustic incident signal, which is mostly distributedin the middle and high frequency bands, is maintained.

The graph of FIG. 3 includes three plot lines 310, 320, and 330. Aweight applied to a signal in the low frequency band decreases from thefirst plot line 310 to the third plot line 330. As an example, amanufacturer or a user of the apparatus 100 or 200 may select afrequency weighting filter for the apparatus 100 or 200, from amongvarious types of frequency weighting filters. The frequency weightingfilter may be selected based on whether the frequency weighting filteris to be used alone or to be installed in a device, and frequencyresponse characteristics in a speaker according to a sound qualitytuning filter. The manufacturer or user may select the frequencyweighting filter that minimizes a distortion of a voice in a generalphone call while maximizing an output limitation of an acoustic incidentsignal, for the apparatus 100 or 200.

FIG. 4 shows graphs for comparing a received signal before and afterpassing through the filter unit 110 or 220 of FIG. 1 or 2. In thegraphs, a horizontal axis indicates time and a vertical axis indicatesan energy value.

The upper graph of FIG. 4 shows a received signal, i.e. a decoded PCMsignal. Signals 410 and 430 illustrated in pillar shapes in the middleof the upper and lower graphs of FIG. 4 indicate acoustic incidentsignals and other signals 420 and 440 other than the signals 410 and 430indicate voice signals.

In FIG. 4, comparing the signal 430 in the lower graph and the signal410 in the upper graph, it can be seen that energy values of the signals410 and 430, i.e., the acoustic incident signals, are similar. However,comparing the signals 420 and 440, i.e., the voice signals, it can beseen that an energy value of the signal 440 is lower than an energyvalue of the signal 420. In other words, the energy value of the voicesignal in the low frequency band is decreased by passing through thefrequency weighting filter, and the energy value of the acousticincident signal in the middle and high frequency bands is not decreased.

In order to classify the acoustic incident signal 410 from among thesignals by using the upper graph of FIG. 4, an energy value higher than−12 db is used as a reference energy value. On the other hand, in orderto classify the acoustic incident signal 430 among the signals by usingthe lower graph of FIG. 4, an energy value higher than −18 db is used asa reference energy value. In other words, the energy value of the voicesignal is lower after being filtered by the filter unit 110 or 220 thanbefore being filtered, and thus a difference between the energy valuesof the voice signal and the acoustic incident signal increases.Accordingly, the reference energy value used to classify the voicesignal from the acoustic incident signal can be decreased.

FIG. 5 is a graph showing a signal output from the output unit 250 ofFIG. 2. In the graph of FIG. 5, a horizontal axis indicates time andvertical axis indicates an energy value.

As described above with reference to FIG. 4, the energy value of thevoice signal is lower after being filtered by the filter unit 110 and220 than before being filtered. Thus, the reference energy value used toidentify the acoustic incident signal is decreased. Since the referenceenergy value is decreased, a gain value, which is a real number between0 and 1 and used to adjust the energy value of the acoustic incidentsignal to the reference energy value, is decreased.

Accordingly, when the decreased gain value is applied to the acousticincident signal from among the received signals, i.e., the decoded PCMsignals, the energy value of the acoustic incident signal is decreasedto the reference energy value, and the energy value of the voice signalis maintained. Thus, the energy value of the acoustic incident signal isless than the energy value of the voice signal.

Such is illustrated in FIG. 5, wherein signals concentrated in thecenter indicate acoustic incident signals 510, and signals other thanthe acoustic incident signals 510 indicate voice signals 520. In FIG. 5,it can be seen that energy values of the acoustic incident signals 510are less than energy values of the voice signals 520.

FIG. 6 is a flowchart illustrating a method of removing an acousticincident signal, according to an exemplary embodiment. Referring to FIG.6, the apparatus 100 or 200 filters a decoded received signal by using afrequency weighting filter, in operation 610. The frequency weightingfilter may give a higher weight from a low frequency band to a highfrequency band, and may be applied in a frequency band of 4 KHz orbelow.

The apparatus 100 or 200 determines whether an energy value of thefiltered signal exceeds a reference energy value, in operation 620.Specifically, the apparatus 100 or 200 may obtain an average energyvalue according to frames of the filtered signal in a time domain. Theapparatus 100 or 200 detects a time band of a signal having an averageenergy value that exceeds the reference energy value, in operation 630.That is, if the average energy value of the filtered signal exceeds thereference energy value, the apparatus 100 or 200 obtains a gain valuefor adjusting the average energy value of the filtered signal to thereference energy value according to frames.

In operation 640, the apparatus 100 or 200 applies the gain value to thereceived signal having the time band, in which the average energy valueexceeds the reference energy value, according to frames.

According to the exemplary embodiments, an acoustic incident signalgenerated during a phone call may be efficiently removed.

While not restricted thereto, exemplary embodiments can also be embodiedas computer readable codes on a computer readable recording medium. Thecomputer readable recording medium is any data storage device that canstore data which can be thereafter read by a computer system. Examplesof the computer readable recording medium include read-only memory(ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppydisks, optical data storage devices, etc. The computer readablerecording medium can also be distributed over network coupled computersystems so that the computer readable code is stored and executed in adistributed fashion. Also, functional programs, codes, and code segmentsfor accomplishing exemplary embodiments can be easily construed byprogrammers skilled in the art to which the present invention pertains.Moreover, while not required in all aspects, one or more units of theapparatus 100 or 200 for removing an acoustic incident signal caninclude a processor or microprocessor executing a computer programstored in a computer-readable medium.

While aspects have been particularly shown and described with referenceto exemplary embodiments thereof, it will be understood by those ofordinary skill in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims. The exemplary embodimentsshould be considered in descriptive sense only and not for purposes oflimitation. Therefore, the scope of the invention is defined not by thedetailed description of exemplary embodiments, but by the appendedclaims, and all differences within the scope will be construed as beingincluded in the present invention.

What is claimed is:
 1. A method of processing a signal, the methodcomprising: filtering a decoded signal, by using a different weight foreach of frequency bands; detecting whether an energy value of thefiltered signal exceeds a reference energy value, in unit of frames; andapplying a gain value to the decoded signal in a detected frame.
 2. Themethod of claim 1, wherein the filtering is performed by using afrequency weighting filter.
 3. The method of claim 2, wherein thefiltering by using the frequency weighting filter comprises filteringthe decoded signal in a frequency band of 4 KHz or lower by using thefrequency weighting filter.
 4. The method of claim 1, wherein thefiltering comprises filtering the decoded signal by applying increasingweights from a low frequency band to a high frequency band.
 5. Themethod of claim 1, further comprising outputting the filtered signal towhich the gain value is applied and remaining filtered signal having anenergy value that does not exceed the reference energy value after beingfiltered, together.
 6. The method of claim 1, wherein the detectingcomprises: calculating an average energy value of the filtered signal ina time domain, for each frame; and detecting a frame in which theaverage energy value of the filtered signal is greater than thereference energy value.
 7. The method of claim 6, further comprising:calculating a value for adjusting the average energy value of thefiltered signal to the reference energy value in the detected frame,wherein the applying the gain value comprises applying the calculatedvalue on the decoded signal in the detected frame as the gain value. 8.The method of claim 7, wherein the gain value is a positive real numberless than
 1. 9. The method of claim 1, further comprising: decoding thesignal to a pulse code modulation (PCM) signal, wherein the filteringcomprises filtering the PCM signal, and the applying the gain valuecomprises applying the gain value to the PCM signal in the detectedframe.
 10. A non-transitory computer readable recording medium havingrecorded thereon a program executable by a computer for performing themethod of claim
 1. 11. An apparatus for processing a signal, theapparatus comprising: a filter unit configured to filter a decodedsignal, by using a different weight for each of frequency bands; adetecting unit configured to detect whether an energy value of thefiltered signal exceeds a reference energy value, in unit of frames; anda gain applying unit configured to apply a gain value to the decodedsignal in a detected frame.
 12. The apparatus of claim 11, wherein thefilter unit filters the decoded signal by using a frequency weightingfilter.
 13. The apparatus of claim 12, wherein the filter unit filtersthe decoded signal in a frequency band of 4 KHz or lower by using thefrequency weighting filter.
 14. The apparatus of claim 11, wherein thefilter unit is configured to filter the decoded signal by applyingincreasing weights from a low frequency band to a high frequency band.15. The apparatus of claim 11, further comprising an output unit whichoutputs the filtered signal to which the gain value is applied andremaining filtered signal, having an energy value that does not exceedthe reference energy value after being filtered, together.
 16. Theapparatus of claim 11, wherein the detecting unit calculates an averageenergy value of the filtered received signal in a time domain, for eachframe, and detects a frame in which the average energy value of thefiltered signal is greater than the reference energy value.
 17. Theapparatus of claim 16, wherein: the detecting unit calculates a valuefor adjusting the average energy value of the filtered signal to thereference energy value in the detected frame; and the gain applying unitapplies the calculated value to the decoded signal in the detected frameas the gain value.
 18. The apparatus of claim 17, wherein the gain valueis a positive real number below
 1. 19. A method of processing a signal,the method comprising: filtering a decoded signal, by using a differentweight for each of frequency bands; detecting, performed by using aprocessor, whether an energy value of the filtered signal exceeds areference energy value, in unit of frames; and adjusting a volume of thedecoded signal in a detected frame.
 20. A non-transitory computerreadable recording medium having recorded thereon a program executableby a computer for performing the method of claim 19.